Adhesive composition

Abstract

A novel low odor two-component acrylic-epoxy adhesive composition and the method of making thereof.

Description

ADHESIVE COMPOSITION Background of the Invention

[0001] In the automotive industry, adhesives are used in the assembly of various components in which these components are bonded to each other or to other parts of the vehicle. In the assembly process of closures (doors, hood and deck lids), some manufacturers require the adhesive to obtain handling strength via a room temperature curing process 15 minutes before the parts enter the high heat of the E- Coat ovens which can cause part distortion of the panels that are not securely bonded. The adhesive joint must also withstand the high heat of the paint and E- Coat ovens during the assembly of the vehicle. It is a growing trend among automotive manufacturers to consider hem flange joints to be a crash critical component of the vehicle. This is due to crash tests and real-world crash events where closures with adhesively bonded hem flange joints have unzipped or separated during a high-speed crash event. Therefore, room-temperature curing adhesives with heat resistance and impact peel strength are required for the closure application. Typically, the adhesive composition is a two-component epoxy-acrylic hybrid for attaining rapid cure and heat resistance. However, these compositions are usually quite brittle and don’t afford the required impact peel strengths.

[0002] Historically, several families of reactive and non-reactive tougheners have been used in the two-component epoxy acrylic hybrid adhesives. One of the most effective and popular reactive tougheners is methacrylate terminated butadiene rubber or methacrylate terminated butadiene acrylonitrile rubber. While this family of reactive tougheners is very effective at imparting impact resistance, they have a very poor supply chain position in that there is only one source of their manufacturing globally. In addition, the manufacturing of these materials is hazardous with negative environmental effects.

[0003] Inventors of the present invention have previously discovered that a two- component hybrid adhesive composition with at least one methacrylate monomer and at least one methacrylate-terminated toughener having a Tg of 0oC or less showed good impact peel resistance after e-coat oven exposure. The invention was disclosed in PCT / US23 / 024257, incorporated herein by reference in its entirety. One drawback in that composition, however, is the perceived offensive odor of the acrylic monomers. While others in the art have attempted to use low odor and low vapor 1   pressure monomers in similar compositions, the results have not been desirable mainly because of the compatibility issues between the low odor and low vapor pressure monomers and the tougheners used in the composition. Therefore, there is a need to arrive at a low odor composition while maintaining all the good qualities of the two-component hybrid composition such as a high level of impact peel strength. Summary of the Invention

[0004] The present invention provides a novel two-component epoxy-acrylic hybrid adhesive composition having a Part A component and a Part B component. The Part A component comprises a) at least one methacrylate monomer wherein the vapor pressure of the methacrylate monomer is less than 10 Pa at 20oC; and b) at least one methacrylate-terminated toughener having a Tg of 0oC or less; and the Part B component comprises at least one epoxy resin; and an oxidizing agent. Detailed Description of the Invention

[0005] The inventors of the present invention have found that it is possible to achieve an epoxy-acrylic adhesive having rapid curing at room temperature while having excellent impact peel strength, even after exposure to high-temperature conditions, and with low odor. The two-component epoxy-acrylic adhesive composition of the present invention has two parts: Part A component and Part B component. Part A component:

[0006] Part A of the adhesive composition comprises at least one methacrylate monomer. The methacrylate monomer is preferably one with low odor and very low vapor pressure typically less than 10 Pa at 20oC, preferably less than 8 Pa at 20oC, and more preferably less than 6 Pa at 20oC, and most preferably less than 5 Pa at 20oC. In some preferred embodiments of the present invention, the methacrylate monomers used in Part A will have the general chemical structure of either Formula I and / or Formula II: 2

[0007] In one preferred embodiment, the methacrylate monomer contains less than 0.5 wt. %, preferably less than 0.1 wt. %, and most preferably less than 0.01 wt. % of methacrylic acid based on the total weight of the methacrylate monomer.

[0008] In another preferred embodiment, Part A comprises two or more methacrylate monomers.

[0009] In an even more preferred embodiment, the methacrylate monomers used in the present invention are selected from isopropylideneglycerol methacrylate, glycerol formal methacrylate, or any mixture thereof. If a mixture is used, the mass ratio between isopropylideneglycerol methacrylate and glycerol formal methacrylate in such embodiment can be between 3:1 to 1:3 and preferably between 2:1 to 1:2, and more preferably 1:1. 3

[0010] The methacrylate monomer or monomers preferably represent 28-45 wt. %, preferably 30-38 wt.% of Part A, and more preferably 33-35 wt.%, all based on the total weight of Part A.

[0011] Part A also comprises at least one toughener, preferably a methacrylate- terminated toughener as disclosed in PCT / US23 / 024257. In a preferred embodiment, the toughener comprises at least one polyether as part of its backbone.

[0012] In preferred embodiments, the toughener has a Tg of 0oC or less Tg of - 20oC or less, more preferably -40oC or less.

[0013] In one preferred embodiment, the at least one toughener is a toughener prepared by reacting a polyether polyol with a polyisocyanate in a ratio such that the resulting polymer is an NCO-capped polymer, followed by end-capping with a hydroxyalkyl ester of methacrylic acid. The polyether polyol may be a diol or triol, with diols being preferred. In another preferred embodiment, the polyol is a poly(C2- C6-alkylene oxide) diol, with C2, C3and C4being preferred, and C4being particularly preferred [i.e. poly(tetramethylene oxide)glycol or PTMEG].

[0014] In yet another preferred embodiment, the polyether polyol is selected from PTMEG’s having molecular weights from 1,000 to 3,000 Da, preferably from 1,500 to 2,500 Da, and more preferably about 2,000 Da. Equivalent and molecular weights are measured by gel permeation chromatography (GPC) using the method and equipment recited in the Examples section.

[0015] The toughener may also comprise a low molecular weight (< 250 Da) polyol having functionality of 3 or 4, such as trimethylol propane. If present, the low molecular weight polyol is preferably used at 0.1-3 wt.%, more preferably 0.25-1 wt.%, particularly preferably 0.5 wt.%, based on the total weight of the toughener. In a preferred embodiment, the toughener comprises trimethylol propane at 0.1-3 wt.%, more preferably 0.25-1 wt.%, most preferably 0.5 wt.%, based on the total weight of the toughener.

[0016] The polyisocyanate may be aliphatic or aromatic, with aliphatic being preferred. In one embodiment, the polyisocyanate is a diisocyanate. In another embodiment, the polyisocyanate is an aliphatic diisocyanate. Examples include hexamethylene diisocyanate (HDI), isophorone diisocyanate, methylene dicyclohexyl diisocyanate.

[0017] The hydroxyalkyl ester of methacrylic acid used in end capping is preferably a C2-C6-hydroxyalkyl ester, more preferably C2-C4-hydroxyalkyl, even 4   more preferably C2-C3-hydroxyalkyl, with C2-hydroxyalkyl being the most preferred, in particular hydroxyethyl methacrylate (HEMA).

[0018] The toughener may also be made by reacting the polyether polyol with the polyisocyanate, in the presence of a polyurethane catalyst to produce an NCO- terminated prepolymer. The prepolymer is then reacted with a hydroxyalkyl ester of methacrylic acid, resulting in end-capping.

[0019] In a preferred embodiment, the toughener is made by reacting PTMEG with HDI, in the presence of a polyurethane catalyst to produce an NCO-terminated prepolymer. The prepolymer is then reacted with HEMA, resulting in end-capping.

[0020] In a preferred embodiment, the toughener has a number average molecular weight (Mn) of 6,119 Da. In another preferred embodiment, the PTMEG has a molecular weight of 2,000 Da, and the toughener has a number average molecular weight (Mn) of 6,119 Da. In yet another preferred embodiment, the toughener has a weight average molecular weight (Mw) of 15,084 Da.

[0021] Part A typically comprises 10-30 wt.%, more preferably 15-25 wt.%, particularly preferably 17-24 wt.% of the toughener, based on the total weight of Part A. In a preferred embodiment, the toughener is made by reacting an aliphatic polyether diol with an aliphatic diisocyanate.

[0022] Part A may also comprise a phosphorus-containing compound, as disclosed in PCT / US23 / 024257, selected from monoesters of phosphonic, mono- and di-esters of phosphonic and mono-, di- and tri-esters of phosphoric acid having one unit of vinyl or allylic unsaturation present.

[0023] Examples of the phosphorus-containing compound include phosphoric acid; 2-methacryloyloxyethyl phosphate; bis-(2-methacryloxyloxyethyl)phosphate; 2- acryloyloxyethyl phosphate; bis-(2-acryloyloxyethyl)phosphate; methyl-(2- methacryloyloxyethyl)phosphate; ethyl methacryloyloxyethyl phosphate; methyl acryloyloxyethyl phosphate; ethyl acryloyloxyethyl phosphate; propyl acryloyloxyethyl phosphate, isobutyl acryloyloxyethyl phosphate, ethylhexyl acryloyloxyethyl phosphate, halopropyl acryloyloxyethyl phosphate, haloisobutyl acryloyloxyethyl phosphate or haloethylhexyl acryloyloxyethyl phosphate; vinyl phosphonic acid; cyclohexene-3-phosphonic acid; (α-hydroxybutene-2 phosphonic acid; 1-hydroxy-1- phenylmethane- 1,1-diphosphonic acid; 1-hydroxy- 1-methyl-1-disphosphonic acid: 1-amino-1phenyl-1,1-diphosphonic acid; 3-amino-3-hydroxypropane-1,1- disphosphonic acid; amino-tris(methylenephosphonic acid); gamma-amino- 5   propylphosphonic acid; gamma-glycidoxypropylphosphonic acid; phosphoric acid- mono-2-aminoethyl ester; allyl phosphonic acid; allyl phosphinic acid; β- methacryloyloxyethyl phosphinic acid; diallylphosphinic acid; β- methacryloyloxyethyl)phosphinic acid and allyl methacryloyloxyethyl phosphinic acid. Preferred phosphorus compounds are 2-hydroxyethylmethacrylate phosphate and phosphonated (meth)acrylic monomer.

[0024] Part A may also comprise a tertiary amine radical initiator as disclosed in PCT / US23 / 024257. Preferred examples include N,N-dimethyl aniline, N,N- dimethylaminomethylphenol and N,N-dimethyl-p-toluidine, with N,N-dimethyl-p- toluidine being the preferred initiator. Part B component

[0025] Part B comprises at least one epoxy resin. Suitable epoxy resins include the diglycidyl ethers of polyhydric phenol compounds such as resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (1,1- bis(4-hydroxylphenyl)-1- phenyl ethane), bisphenol F, bisphenol K, bisphenol M, tetramethylbiphenol, diglycidyl ethers of aliphatic glycols and polyether glycols such as the diglycidyl ethers of C2-24 alkylene glycols and poly(ethylene oxide) or poly(propylene oxide) glycols; polyglycidyl ethers of phenol-formaldehyde novolac resins, alkyl substituted phenol formaldehyde resins (epoxy novalac resins), phenolhydroxybenzaldehyde resins, cresol-hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins and dicyclopentadiene- substituted phenol resins, and any combination thereof. Suitable diglycidyl ethers include diglycidyl ethers of bisphenol A resins such as are sold by Olin Corporation under the designations D.E.R.®330, D.E.R.®331, D.E.R.®332, D.E.R.®383, D.E.R.®661 and D.E.R.®662 resins.

[0026] In a preferred embodiment, the at least one epoxy resin comprises a reaction product of epichlorohydrin and bisphenol A. In another preferred embodiment, the at least one epoxy resin comprises a liquid reaction product of epichlorohydrin and bisphenol A.

[0027] In a preferred embodiment, the at least one epoxy resin comprises an epoxy resin that is a liquid reaction product of epichlorohydrin and bisphenol A, having an epoxide equivalent weight of 182-192 g / eq (as measured according to ASTM D-1652), an epoxide percentage of 22.4-23.6 % (as measured according to ASTM D-1652), an epoxide group content of 5,200-5,500 mmol / kg (as measured 6   according to ASTM D-1652), and a viscosity at 25oC of 11,000-14,000 mPas (as measured according to ASTM D-445).

[0028] In another preferred embodiment, the at least one epoxy resin comprises a bisphenol A-based epoxy resin with an epoxy equivalent weight of approximately 352.5 g / equivalent.

[0029] Part B comprises 20 to 80 wt.%, preferably 20 to 60 wt.%, more particularly preferably 25 to 40 wt.% of the at least one epoxy resin, based on the total weight of Part B.

[0030] Part B may also comprise an oxidizing agent as disclosed in PCT / US23 / 024257. Examples of such oxidizing agents include organic peroxides, such as benzoyl peroxide and other diacyl peroxides, hydroperoxides such as cumene hydroperoxide, peresters such as β-butylperoxybenzoate; ketone hydroperoxides such as methyl ethyl ketone hydroperoxide, organic salts of transition metals such as cobalt naphthenate, and compounds containing a labile chlorine such as sulfonyl chloride. The most preferred oxidizing agent is benzoyl peroxide.

[0031] The oxidizing agent, preferably organic peroxide such as benzoyl peroxide, is preferably present in Part B at 3-10 wt.%, more preferably 5-9 wt.%, based on the total weight of Part B. Optional ingredients

[0032] The adhesive composition of the present invention may contain additional optional ingredients, such as, for example: stabilizers / free-radical scavengers being added to both Part A and Part B, to extend shelf-life of the unmixed parts. Examples of stabilizers / free-radical scavengers include 1, 3, 5-trimethyl-2,4,6-tris (3,5-di-tert- butyl-4-hydroxybenzyl) benzene, di-ethylhydroxy amine (DEHA), butylated hydroxy toluene (BHT), methyl ether of hydroquinone, hydroquinone, benzoquinone, naphthoquinone, hydroxyl amine, and nitrile oxides. The optional ingredients may also include fillers such as wollastonite, talc, fumed silica, calcium carbonate and glass.

[0033] Part A may optionally comprise cross-linkers, such as divalent metal salts of methacrylic acid, such as zinc dimethacrylate, calcium dimethacrylate, magnesium dimethacrylate, or mixtures of these. Part A may also optionally comprise an additional toughener. Suitable additional tougheners are rubber based, such as 7   acrylate-based tougheners, butadiene-based tougheners, acrylonitrile-butadiene- based tougheners, chlorinated or chlorosulphonated polyethylenes, block copolymers of styrene and conjugated dienes (SBS, SIS), ethylene acrylic elastomers, core-shell graft copolymers. Specific examples can be a copolymer of 2-propeneoic acid, 2-methyl-, methyl ester with 1,3-butadiene.

[0034] If used, the additional rubber-based toughener is preferably used in Part A at 2-24 wt.%, more preferably 7.5-18.5 wt.%, more particularly preferably 10-15.75 wt.%, based on the total weight of Part A.

[0035] Additional optional ingredients may include, for example, adhesion promoters, pigments, thixotropic agents, wetting agents, reactive diluents, antioxidants, inhibitors, and stabilizers. These ingredients may be used in an amount commonly known to one skilled in the art to achieve their intended purposes. Method of manufacture

[0036] The at least one toughener is manufactured by a method as disclosed in PCT / US23 / 024257 which includes the steps: (1) mixing a polyetherpolyol and a polyisocyanate; (2) adding a catalyst capable of catalyzing the reaction of a hydroxyl group with an isocyanate group, to form an isocyanate terminated prepolymer; and (3) reacting the isocyanate prepolymer is then reacted with a hydroxyalkyl ester of methacrylic acid, such that the isocyanate groups are capped with the hydroxyalkyl ester of methacrylic acid. The reactions in steps (2) and (3) are typically carried out under vacuum or under a neutral atmosphere, such as nitrogen or argon.

[0037] The catalyst is preferably selected from Lewis bases and Lewis acids. Suitable catalysts include tertiary amines, including diazabicyclo[2.2.2]octane, 2,4,6- tris((dimethylamino)methyl)phenol, DMDEE (2,2'-Dimorpholinodiethylether), imidazoles, such as 4-methylimidazole), triethanolamine, and organometallic catalysts, in particular organotin compounds, such as dibutyl tin dilaurate, dioctyltindineodecanoate, and other metal catalysts such as tetrabutyltitanate, zirconium acetylacetonate, and bismuthneodecanoate. Method of use

[0038] In use, the adhesive Part A and Part B are mixed to homogeneity and applied immediately. The mixing ratio of Part A to Part B is preferably 2:1 to 10:1, with 4:1 being particularly preferred. 8

[0039] Suitable substrates include, for example, electrogalvanized steel, hot dipped galvanized steel, cold rolled steel, and aluminum. EXAMPLES

[0040] The following non-limiting examples are provided to further describe the present invention. Ingredients are listed in Table 1 below:

[0041] Table I. Ingredients for both Comparative and Inventive Examples Comparative Inventive Inventive Inventive Example Example 1 Example 2 Example 3 0 2 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 5 00 0 0 0 0 0 0 0 0 0 0 0 00

[0042] Details of these ingredients and their sources are provided below: Part A Ingredients  Trade Name  Chemical Name  /  description  Available from  Visiomer THFMA  Tetrahydrofurfuryl methacrylate  Evonik  BISOMER IPGMA  Isopropylideneglycerol Methacrylate  GEO Specialty Chemicals  Visiomer GLYFOMA  Glycerol formal methacrylate  Evonik  Visiomer CHMA  cyclohexyl methacrylate  BASF  Visiomer Terra IBOMA  isobornyl methacrylate  Evonik  Dymalink 708  Zinc Dimethacrylate  Total  /  Cray Valley  Novel elastomeric urethane toughener  capped hydroxy‐functional methacrylate,  RAM HEMA  disclosed in US 8,747,605B2   DuPont  Methacrylate Terminated Butadiene‐ Hypro 1300X33LC VTBNX  Acrylonitrile liquid rubber  Huntsman  Kane Ace B‐564  MBS core shell rubber  Kaneka  MIRAMER M2101  ethoxylated bis‐A dimethacrylate  Miwon  Visiomer HEMA‐P 100  HEMA Phosphate   Evonik  Methacrylic Acid  Methacrylic Acid  Sigma Aldrich  X‐821‐2000  Methacryoyloxy Ethyl Phthalate  Esstech, Inc.  Dynasylan 6498  vinyl oligomeric siloxane  Evonik  N,N‐Dimethyl‐p‐toluidine  N,N‐Dimethyl‐p‐toluidine  Aceto, Corp.  3, 3', 3'', 5, 5', 5''‐ HEXA‐ TERT. ‐ BUTYL‐ ALPHA, ALPHA', Ethanox 330 ALPHA''‐(MESITYLENE, 4, 6‐ TRIYL) TRI‐ PARA‐ CRESOL SI Group  DEHA  Sigma Aldrich  Nyad 200 Imerys  CIM TALC 7  Talc  Kish Company, Inc.  GL0191B4 / 212‐300  10 mil glass bead spacers  MO‐SCI Corp.  Cab‐O‐Sil Ultrabond 5780  fumed silica  Cabot    Part B Ingredients  Trade Name  Chemical Name  Available from  Luperox ATC‐50  Benzoyl peroxide paste in plasticizer  Arkema  Cab‐O‐Sil Ultrabond 5780  fumed silica  Cabot  Heliogen Green D 8730  green pigment  BASF  Ti‐Pure R900  titanium dioxide pigment  Chemours  Hubercarb Q325  calcium carbonate  Huber Engineered Materials  Hakuenka CCR  Precipitated calcium carbonate  Shiraishi Kogyo Kaisha, LTD  DER 331  epoxy resin, EEW 182  Olin  DER 732  Epoxy diluent, EEW 320  Olin  Lite 2020  Cashew nutshell extract  Cardolite  XZ92579  epoxy resin, EEW 335  Olin  BHT  butylated hydroxy toluene  Sigma Aldrich  10

[0043] Table 2 lists the vapor pressure of various methacrylates used in the Examples:

[0044] Table 2. Vapor pressure of methacrylates used in the Examples. Visiomer THFMA 27 Pa at 20°C BISOMER IPGMA 4 Pa at 20°C Visiomer GLYFOMA 5 Pa at 20°C Visiomer CHMA 18.4 Pa at 20°C Visiomer Terra IBOMA 7.5 Pa at 20°C

[0045] All details of making the composition Examples and the testing thereof are disclosed in PCT / US23 / 024257, incorporated again herein by reference in its entirety. All physical characteristics, such as impact peel, lap shear, and T-peel tests show comparable results between the Comparative Example and the Inventive Examples.

[0046] In addition, all Examples were also subject to Odor Ranking test using ASTM D4339 with Comparative Example as the reference sample. In this test, a panel of 3 people ranked the odor of each example in comparison to the reference. Each example was characterized by each panel member as having odor less than, equal to, or greater than the reference example The Odor Ranking test results are summarized in Table 3.

[0047] Table 3. ASTM D4339 Odor Ranking test results as compared to Comparative Example Inventive Ex 1 <

[0048] As showrylate is used, Inventive Examples 1 and 2 demonstrated less odor than the Comparative Example where a relatively higher vapor pressure methacrylate is used. It is noted that 11   Inventive Example 3 has essentially the same odor level as the Comparative Example. This is caused by the presence of odor in the toughener itself used in Part A. This toughener carried odor is recognizable in the presence of low odor monomers. The urethane toughener used in Inventive Examples 1-2 do not carry such odor. 12

Claims

Claims 1. A two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) at least one methacrylate monomer wherein the vapor pressure of the methacrylate monomer is less than 10 Pa at 20oC; and b) at least one methacrylate-terminated toughener having a Tg of 0oC or less; and the Part B component comprises at least one epoxy resin; and an oxidizing agent.

2. The adhesive composition of Claim 1 wherein the Part A component further comprising a phosphorus-containing compound selected from monoesters of phosphonic, mono and diesters of phosphonic and phosphoric acids.

3. The adhesive composition of Claim 2 wherein the Part A component further comprises a tertiary amine radical initiator.

4. The adhesive composition of any one of the preceding claims wherein the vapor pressure of the methacrylate monomer is less than 6 Pa at 20oC.

5. The adhesive composition of any one of the preceding claims wherein the Part A component comprises 28-45 wt.% of methacrylate monomer, based on the total weight of Part A component.

6. The adhesive composition of any one of the preceding claims wherein the methacrylate monomer has chemical structure of one of Formula I or II 13   7. The adhesive composition of any one of the preceding claims wherein the methacrylate monomer is isopropylideneglycerol methacrylate, glycerol formal methacrylate, or a mixture thereof.

8. The adhesive composition of any one of the preceding claims wherein the toughener comprises at least one polyether as part of its backbone.

9. The adhesive composition of any one of the preceding claims wherein the at least one epoxy resin comprises a reaction product of epichlorohydrin and bisphenol A.

10. The adhesive composition of any one of the preceding claims wherein Part B component comprises 20 to 80 wt.% of the at least one epoxy resin, based on the total weight of Part B component. 14   11. The adhesive composition of any one of the preceding claims wherein the oxidizing agent is benzoyl peroxide.

12. The adhesive composition of any one of the preceding claims wherein Part B component comprises 3-10 wt.% of the oxidizing agent, based on the total weight of Part B component.

13. The adhesive composition of any one of the preceding claims wherein the one methacrylate-terminated toughener is an elastomeric urethane toughener capped with hydroxy-functional methacrylate.

14. The adhesive composition of any one of claim 1 to claim 12, wherein the one methacrylate-terminated toughener is butadiene-acrylonitrile liquid rubber based toughener.

15. A two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) 33 wt.% to 35 wt.% of glycerol formal methacrylate; based on the total weight of Part A component; and b) about 23 wt. % of an elastomeric urethane toughener capped with hydroxy-functional methacrylate having a Tgof 0oC or less, based on the total weight of Part A component; and the Part B component comprises at least one epoxy resin; and an oxidizing agent. 15

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